Improve vector constructor documentation

[rbeezer]

This is a documentation-only patch, other than some minor whitespace clean-up in the code. It brings the documentation of the vector() constructor in line with the code. Specifically the handling of integer arguments (degree), the absence of entries (creating zero vectors), and some subtleties with dictionary input.

It suggests some code changes: negative integer arguments, more care with dictionary input, and a new zero_vector() constructor, which will go on another ticket (see #10364).

[novoselt]

Looks like a nice improvement, except that dictionary-related parts seem to be weird, but this is addressed by another ticket.

In the original patch "INPUT" is "glued" to the numbered list above, so I indented the list to separate them. Also, I like when "OUTPUT" block looks the same as "INPUT" and in this particular case it really makes sense, I think, because the output description is so long. So I have added a blank line as well.

If you agree with the changes, please switch to positive review!

[rbeezer]

Andrey,

Thanks for the review and fixes. I'd noticed the "gluing" but had not experimented with a fix. I think I have a couple more tickets in-progress where I need to make that change as well.

I'm conflicted on the format of the OUTPUT block header and vacillate between the two options. Your change is fine.

Reviewer patch applies, tests, docbuilds just fine. So I'll flip this to positive review.

Thanks again, Rob

Release Manger

Apply original patch and then reviewer patch.